Also worth looking at the self-installation option with BT Openworld as this will reduce the initial outlay.
I believe you can now also purchase your own ADSL modem vs. using the unreliable Alcatel Frog which they supply. I ditched my Alcatel box after 12 months of tearing hair out. Not had one failed connection or problem in the past 6 months.
It is not technically difficult to self-install.
www.btopenwoe.co.uk may be worth a visit - some good advice if you dig around on the forums.